This invention relates to a power assisted, manually operated vehicle such as a bicycle or the like and more particularly to an improved drive arrangement therefore.
There is considerable interest in the utilization of power assist mechanisms for manually powered vehicles such as bicycles. By utilizing a power assist, it is possible to widen the use of such vehicles and permit their utilization by individuals who might not otherwise be able to ride or operate them.
Generally, the power assist mechanism is provided by a prime mover such as a internal combustion engine or an electric motor. In one form of such vehicle, the amount of power assist provided by the prime mover is varied in response to the input force from the operator.
These mechanisms employ a first transmission that drives a transfer shaft from both the pedal operated mechanism of the vehicle and the prime mover. The transfer shaft then drives the rear wheel through a final drive transmission. Frequently, the transfer shaft is disposed so that it is in substantial alignment with the engine crankshaft and may in fact be incorporated in a common drive with it. This requires the prime mover and its transmission to be juxtapose to this same general location. As a result, the drive mechanism for the vehicle is located relatively low and close to the ground. This further complicates the frame structure for the vehicle.
That is, if the vehicle is a bicycle, the chain stays are positioned in surrounding relationship to the final drive and are also located relatively low in the vehicle. This gives rise to ground clearance and other disadvantages.
It is, therefore, a principal object of this invention to provide an improved transmission arrangement for a power assisted, manually powered vehicle.
It is a further object of this invention to provide an improved transmission arrangement for a power assisted, manually operated vehicle wherein the transfer drive and the power assist are located above the axis of the crankshaft so as to improve the frame construction and reduce the number of low components so as to offer improvements in ground clearance.
It is a still further object of this invention to provide an improved transmission arrangement for a power assisted, manually powered vehicle wherein the power assist mechanism can be located at a relatively high location so as to improve ground clearance.
In power assisted, manually operated vehicles, it is generally the practice to employ in the transmission from the crank mechanism to the driven wheel a step-up transmission. This permits the rear wheel to be driven at a faster speed of rotation than the manually operated crankshaft.
However, the power assist mechanism generally includes a prime mover, as of the aforenoted types, that dictates the use of a step-down transmission. Thus, it has been the practice to employ a step-down transmission between the output shaft of the prime mover and the transfer shaft. Since the transfer shaft provides a step-up mechanism, a greater step-down must be utilized in the transmission drive from the prime mover. Thus, the speed of the prime mover drives the rear wheel first through a step-down transmission and then a step-up transmission which is quite inefficient.
It is, therefore, a further object of this invention to provide an improved transmission arrangement for a power assisted, manually operated vehicle.
It is a further object of this invention to provide an improved transmission for a power assisted, manually operated vehicle wherein the entire transmission ratio from the prime mover to the driven wheel is a step-down ratio while the transmission from the manually operated crankshaft to the rear wheel is a step-up transmission.